A method for recovering, from a waste water containing a fluorinated emulsifier, the fluorinated emulsifier by an anion exchange resin (hereinafter referred to as IER) has been known.
For example, a method of adsorbing a fluorinated emulsifier such as ammonium perfluorooctanoate (hereinafter referred to as APFO) on an IER and recovering the fluorinated emulsifier contained in a waste water (hereinafter sometimes referred to as coagulation waste water) resulting from an aqueous dispersion containing a fluorinated polymer and the fluorinated emulsifier, obtained by coagulating the fluorinated polymer in the aqueous dispersion to form coagulum and recovering the coagulum has been known (Patent Documents 1 to 3).
However, the coagulation waste water contains SS (suspended solid) components such as non-coagulated fine particles of the fluorinated polymer and coagulated particles of the fluorinated polymer having small particle sizes which had passed the filter. Accordingly, when the fluorinated emulsifier contained in the coagulation waste water is adsorbed on an IER, the surface of the IER is covered with the SS components, whereby problems arise such that a column packed with the IER is clogged, and the adsorption performance of the IER decreases. If such problems arise, the fluorinated emulsifier may not efficiently be recovered from the coagulation waste water.
To overcome such problems, the following methods have been proposed (Patent Document 4).
(1) A method of adding a nonionic surfactant or a cationic surfactant to the coagulation waste water to stabilize fine particles of polytetrafluoroethylene (hereinafter referred to as PTFE) contained in the coagulation waste water to suppress clogging of the column packed with the IER.
(2) A method for pretreating a coagulation waste water by adding lime water to a coagulation waste water containing a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer (hereinafter referred to as PFA) to adjust the pH to be from 6 to 7.5, adding a metal salt such as aluminum chloride to coagulate non-coagulated PFA, mechanically separating the coagulum, and adjusting the pH of the coagulation waste water to be at most 7 with sulfuric acid.
However, it is not possible by the method (1) to sufficiently suppress clogging of the packed column, the decrease in the adsorption performance of the IER, etc.
The method (2) is not easily conducted. Further, since the SS components cannot sufficiently be removed, if a large amount of the coagulation waste water is treated with the IER, the column packed with the IER will be clogged, and the adsorption performance of the IER will decrease.